Frequency variation indicator circuit



Patented Mar. 4, 1941 UNITED sures PATENT pence T raaonnxcy vanu'rron nvmca'roa Stuart w. Seeley, Bayside, Long nuns, N. y, as-

signcr to Radio Corporation of America, New

York, N. Y, a corporation efDelawarc,

Original application 0mm 11, 1935, Serial no.

Divided and this application Jan 45,413. 14, 1938, Serial No. 1

2 Claims. (Cl. 112-245) In present invention relates to high frequency variation response circuits, and more particularly to frequency response networks of a type utilizing changes in phase relations of primary and secondary circuit voltages which occur in coupled tuned circuits when the applied high frequency energy departs from resonance with the timed circuits. The present application is a division of my copending application Serial No. 45,413, flied Oct. 17, 1935.

In the past frequency variation response circuits have been proposed for many uses. Such uses have involved the indication of frequency departure from a. predetermined frequency value: the maintenance of a resonant circuit at a frequency of a predetermined magnitude; or the utilization of signal energy in a receiver for automatically tuning a resonant circuit to a predetermined frequency. Such proposed circuits have usually employed frequency discriminator networks embodying resonant circuits mistuned by equal frequency values toopposite sides of a predetermined operating frequency. The direct current, component of the rectified output of a discriminator network is utilized, in such prior proposed circuits, to perform the functions referred to above. One of the chief disadvantages of such prior discriminator networks has been the dlfiiculty in aligning the mistuned circuits of the discriminator with the resonant circuits of the receivlnsfl 'ystem which are tuned to the operating frequency.

Accordingly, it may be stated that it is one of the primary objects of my present invention to provide a high frequency variation response network wherein there is not employed side circuits tuned above and below a predetermined center frequency, but wherein the frequency discriminating circuits are tunedto the common operating frequency of the entire system with the result that the aligning of such a discriminator network with other circuits of the receiving system is greatly simplified, and signaling system embodying such discriminator networks are rendered hig y P ctical.

The aforementioned proposals of the prior art have all substantially utilized mlstuned circuits in the discriminator network in such a manner that the differential direct current outprior circuits each mistimed circuit of the discriminator network is connected to a rectifier, nd as the applied frequency departsfrorn resv itself, however, as to both its organization and tentials of coupled tuned circuits. In particular,

nance with the desired operating frequency, the center frequency of the mistuned circuits, either one or the other of the mistuned rectifier-s becomes operative to derive a direct current from 9 the applied signal energy. i

It is, then, one of the important object: of I my present invention to provide a frequency variation response network which functions in an I entirely different manner from such prior pro- 1 I posed circuits, and wherein there is established 1 in the frequency response network a predeteri mined phase difference between a primary and secondary potential of a tuned network embodyi ing primary and secondary circuits, the phase I angle between the primary and secondary po- 1 tentiais varying as the applied energy varies frequency from resonance.

Another important object of the present invention is to provide a method of, and apparatm for, obtaining differential direct current potentials, or currents, whose magnitude and polarity are determined by the amount and the sign, respectively, of the diflerence between an applied frequency and a certain fictitious frequency, and wherein the action depends upon the fact that a 90' phase difference exists between the primary and secondary potentials of a double tuned transformer when energy of the resonant frequency is applied, and that this phase angle varies as the applied frequency varies.

Still other objects of the invention are to improve generally the simplicity and eiliciency of high frequency variation response networks, and more especially to provide such networks in a simple and economical manner which will not only be reliable in operation, but also be readily manufactured and assembled in desired signaling systems.

The novel features which I believe to be characteristic of my invention are set forth inparticularity in the appended claims; the invention method of operation will best be understood ta reference to the following description taken in connection with the drawing. in which I have indicated diagrammatically a circuit tion whereby my invention may be carried into effect.

As stated heretofore, the functioning of the present invention depends upon a predetermined phase relationship which exists between the pothe action depends upon the fact that when a pair of resonant circuits are coupled, and each present invention applied to a visual tuning indicator.

In'the drawing, there is shown a pair of coupled resonant circuits P and S: the circuit P is tuned to a desired frequency by shunt condenser I. while circuit S is tuned to the same frequency brcbndenser 2. The high frequency waves, which are to be applied to the double tuned network P-S. are derived from a source 3 of hkgh frequency waves; and the source may be, for example, a signal generator capable of generating waves having a frequency of about.

465 kc. Such a source includes a device enabling it to be adJusted in frequency so that the frequency of the wavescan be varied, and those skilled in the-art are fully aware of such devices. An amplifier 4 is used to amplify the waves from source 3 prior to their application to circuit P. The numeral 8 designates an oscilloscope of a well known type; the deflector plates being denoted by numeral 6, and the fluorescent screen thereof bearing numeral I.

To visually depict the relations between the voltages across the primary and secondary circuits P and 8 oil and on resonance with the impressed waves from source I, a pair. of the plates 3 are connected across circuit P, while the other pair of plates 6 are connected across circuit 8. Assume, now, that each of circuits P and S is tuned to a predetermined frequency of source I, say 465 to, and waves of that frequency are impressed on amplifier 4 by source 3. A circular pattern I will form on the screen I. This circle was observed to increase, or decrease, in diameter as the amplitude of the waves from source 3 increased, or decreased, respectively. Again, as the frequency of the waves generated by source 3 varied, the shape of pattern 8 was observed to change. The dotted ellipse 8' denotes the appearance of the pattern shape when the frequency of the impressed waves is varied. The degree of coupling between P and S determines whether or not the major axis of the ellipse will.

exceed the diameter of circle 8. Thus, if the coupling is adjusted to criticaivalue, or over, the major axis will be greater as the applied frequency departs from resonance.

It will, therefore, be seen that the shape of the pattern on the screen I is dependent on the phase relations of the voltages applied to plates 6 by circuits P and 8. Changes in amplitude 08, or on, resonance only varies the size of the 4 pattern. Further, a change'of impressed frequency oil resonance with circuits P and S will result in an appreciable change in the form of the pattern I. These relations are understood when it is realized that a 90' phase diflerence exists between the potentials of circults P and S when energy of the resonant frequency is applied, and that this phase angle varies as the applied frequency varies. The oscilloscope 5, then, demonstrates in a visual manner the effect of the applied frequency on the phase relation between the potentials across P and S,and proves that for applied frequencies other than the resonant frequency of circuits P-s the voltages across these two circuits are not in time quadrature.

While I have indicated and described one system for carrying my invention into eifect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organization shown and described, but that many modifications may be made without departing from the scope of my invention, as set forth in the appended claims.

What I claim is? 1. In combination a source of electric waves a predetermined radio frequency, solely two monant circuits coupled to each other and arranged in cascade, the first of said circuits being coupled to said wave source to receive waves therefrom, each of said resonant circuits being exactly mined to the said predetermined frequency, the voltages across said coupled resonant circuits differing 90 in phase when the waves impressed thereon are of the said predetermined frequency, and frequency departure indicating means responsive to a phase angle change between said voltages when the applied waves depart from resonance with said coupled circuits, said means comprising a cathode ray tube provided with a fluorescent screen and two pair of deflection elements, and each pair of said deflection elements being directly, and without the interposition of other electrical elements connected to a respective one of said coupled circuits.

2. In combination with a source of radio freqnency waves including means for varying the 4 frequency thereof; a wave transmission network consisting solely of two coupled circuits each exactly tuned to a common desired frequency, means coupling said source to said network, a resonance indicator device of the cathode ray tube type including a fluorescent screen and two pair of deflection electrodes, one pair of elwtrodes being directly connected to one of said coupled circuits, and the other pair directly to the second circuit; gaid'direct connections being free of any other electrical elements, said screen having a pattern formed thereon whose shape is dependent on the relation between the said desired frequency and that of waves applied to the 

